[unreadable] Rheumatoid arthritis (RA) is an immtmologically mediated, familial, chronically relapsing disease eventually resulting in joint destruction. Understanding inflammatory mediators is critical because these molecules provide approaches for pharmacologic blockade by specific inhibitors and receptor antagonists. Recent rodent models of arthritis have shown that bacterial cell wall polymers can induce acute and chronic arthritis in genetically susceptible rat strains. Parenterally injected peptidoglycanpolysaccharide complexes (PG-APS) induce a systemic inflammatory response consisting of erosive polyarthritis, hepatic granulomas, and anemia. We have shown that experimental inflammatory arthritis is associated with in vivo activation of the kallikrein-kinln system (KKS) in Lewis rats and is selectively inactivated in these susceptible Lewis rats, but not in resistant Buffalo rats. A specific kallikrein inhibitor decreases both the KKS activation and acute inflammatory changes (edema, neutrophil infiltration) and prevented arthritis and the systemic complications (splenomegaly, hepatomegaly, leukocytosis and the acute phase reaction) in the PG-APS model. We now focus on the role of innate immune mechanisms in models of rodent inflammatory arthritis, specifically the interaction of the KKS with monocytes and neutrophils resulting in release of cytokines. We explore two major hypothesis-using approaches new to this laboratory. First, we hypothesize that the lack of high molecular weight kininogen (HK), which is required for activation of plasma kallikrein, is the substrate for release of bradykinin and will modulate the acute and chronic arthritis and systemic inflammation produced by PG-APS in genetically susceptible Lewis rats. We have found that these rats have a single point mutation $511N leading to N-glycosylation which increases the susceptibility of HK to proteolysis. We will examine the mechanisms by which accelerated release of bradykinin and cleaved HK (HKa) in Lewis rats will augment inflammatory cytokine release by the innate immune system, particularly macrophages, stimulated through cellular receptors for bradykinin and HKa on leukocytes. This hypothesis will be explored further using a rat line with a single point mutation in kininogen leading to a block in hepatic secretion and severe plasma deficiency, which we have placed onto the susceptible Lewis genotype. We will also use the human HLA-B27 transgenic rat as a model of "spontaneous" chronic arthritis, which we will treat with a monoclonal antibody to HK. Second, we will compare the degree of inflammation in Lewis vs. Fischer rats with variable degrees of kininogen cleavage I during experimental arthritis and systemic inflammation induced by PG-APS. We will test whether modulation of inflammation by] recombinant HK polypeptides, synthetic peptides, or antibodies to that protein, which are known to inhibit binding of HK or HKa to] leukocytes, can prevent many of the inflammatory changes. We will examine the role of HKa and bradykinin using knockouts of their binding proteins, uPAR and B2R, in murine arthritis and systemic inflammation. If these approaches result in a substantial decrease in arthritis and systemic inflammation, it could lead to the control of rheumatic diseases with potentially fewer side effects than current therapeutic approaches. [unreadable] [unreadable]